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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Mitsubishi VS-50703 Need Advise
My tv does not power up. I was looking at the main board on the mitsubishi
VS 50703 and noticed that I saw clear fluid on the board. An aluminium heat sink is corroiding due to the fluid. Is this what happens when a eletrolitic cap fails, they leak fulid? Can this damage other parts. What do I use to clean the fluid off the board. And what is the best way to tell which part the fulid came from if none of the parts look damaged? Should I replace all the parts in the area? |
#2
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That's coolant from the CRTs.
It's bad news, but usually can be fixed. After you clean the PC boards and got it up and running you need to devise some sort of gutter. The leak is so slow and hard to detect that most of us have decided not to actually fix the leak. It is slow enough that it'll be hard to find, and you can't get new gaskets for it. Iv'e also seen brand new CRTs from Mits leak within a month so that won't do you any good either. I'm hooked up with a seal and gasket company and hopefully this year we will start selling seal kits. These will be of a special low durometer silicone and should never leak. Right now I'm trying to gather up a bunch of these seals so they can be measured. There might be a little money in it, because you gotta fix the RCAs because it screws up the anode cap, and the Mitses will eventually leak too low for proper operation. Right now however, the best solution is a gutter IMO. A couple of manufacturers actually did use gutters. Mits actually did in the past for a few years and NEC also. The only problem with a gutter is that the lead dress will never be the same. It looks a little messy, but it works. The set you got isn't so bad on caps leaking, but they do get high ESR. You should probably repost and ask advice on the best way to clean the board. My method is a paintbrush among other things with acetone, alcohol and then water. After that dry it with a hair dryer. If in doubt, repeat. Sometimes I also freeze it with freeze spray to make the PCB contract and squeeze more of the crap up to the surface and clean it somemore. Wherever it was the worst, take an ohmmeter, preferably one that'll measure up to 20 megohms, and stick the probes right on the PCB about 1 mm. or less apart. It should read infinity. If it reads any conductance, clean it more or it'll get worse. Inspect both boards, and be very very careful with the signal board, it's double sided and easy to break the feedthroughs. Then it gets very hard to fix. I don't care if you got deep pockets and decide to change all three tubes you still need the gutter. You DO NOT want this to happen again. JURB |
#3
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These tubes usually leak a little then stop leaking. Mostly when the sets
have been moved. I have never seen one continue to leak enough to run low on coolant. We have a technique for guttering them that is easy and does not affect wire dress at all. Simply take a short length of outside corner molding, wire tie it to the two mounting screws for the frame of the tubes and make a vertical gutter to the front of the set between the main chassis and the CRT boards. All you have to do is get under the area between the green and blue and green and red tubes where it drips off. Takes two pieces of molding about a foot long, two nylon wire ties, and upsets no wire dress. As for the boards, if the coolant got to the micro, you are likely screwed. Otherwise, look for feed-throughs (dual sided board) that are corroded and repair any damaged traces before bothering to troubleshoot it. The board and the micro are no longer available because of coolant leaks. We use isopropanol or denatured alcohol to clean the boards. I wouldn't bother trying to market seals for these. Anyone who fixes many of them would not bother. If you reseal them after cleaning carefully with a thin layer of silicone sealer and let it cure overnight before refilling it, they never leak again. Mostly we don't bother if they are not continuing to leak. Just gutter it. It is ironic that shortly after they stopped putting gutters in the sets we started seeing leaks. I can't remember ever seeing coolant in one of the old catches they used. They have resumed using them as of a couple of years ago. Leonard "JURB6006" wrote in message ... That's coolant from the CRTs. It's bad news, but usually can be fixed. After you clean the PC boards and got it up and running you need to devise some sort of gutter. The leak is so slow and hard to detect that most of us have decided not to actually fix the leak. It is slow enough that it'll be hard to find, and you can't get new gaskets for it. Iv'e also seen brand new CRTs from Mits leak within a month so that won't do you any good either. I'm hooked up with a seal and gasket company and hopefully this year we will start selling seal kits. These will be of a special low durometer silicone and should never leak. Right now I'm trying to gather up a bunch of these seals so they can be measured. There might be a little money in it, because you gotta fix the RCAs because it screws up the anode cap, and the Mitses will eventually leak too low for proper operation. Right now however, the best solution is a gutter IMO. A couple of manufacturers actually did use gutters. Mits actually did in the past for a few years and NEC also. The only problem with a gutter is that the lead dress will never be the same. It looks a little messy, but it works. The set you got isn't so bad on caps leaking, but they do get high ESR. You should probably repost and ask advice on the best way to clean the board. My method is a paintbrush among other things with acetone, alcohol and then water. After that dry it with a hair dryer. If in doubt, repeat. Sometimes I also freeze it with freeze spray to make the PCB contract and squeeze more of the crap up to the surface and clean it somemore. Wherever it was the worst, take an ohmmeter, preferably one that'll measure up to 20 megohms, and stick the probes right on the PCB about 1 mm. or less apart. It should read infinity. If it reads any conductance, clean it more or it'll get worse. Inspect both boards, and be very very careful with the signal board, it's double sided and easy to break the feedthroughs. Then it gets very hard to fix. I don't care if you got deep pockets and decide to change all three tubes you still need the gutter. You DO NOT want this to happen again. JURB |
#4
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Thank you all for replying, I have a few more questions. Can the coolant be
refilled in the projector lamps? And How would that be done? Where does the coolant usually leak from? What part of the projector lamp? Is using a gutter the only solution? The fluid leaks on the main board, I found a part that was so corroded by the coolant that one of the leads was broken off. Part L932 Coil RF 10mH-k. Do you think this is the cause for the tv not to turn on or do you think the coolant could have damaged more parts. Should I replace every part that has coolant on it? |
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